Some kind of brake hydraulic pressure generating device has a master cylinder, a slave cylinder using a motor as a driving source, and a stroke simulator.
The aforementioned brake hydraulic pressure generating device includes a main hydraulic pressure passage for communication between the master cylinder and each wheel cylinder, a branch hydraulic pressure passage branched from the main hydraulic pressure passage and reaching the stroke simulator, and an on/off valve for opening/closing the branch hydraulic pressure passage.
The aforementioned on/off valve is a normally closed type solenoid valve. As such an on/off valve, there is an on/off valve provided with a first valve mechanism and a second valve mechanism (for example, see JP-2013-227011-A).
In the aforementioned on/off valve having two valve mechanisms, a first valve portion of the first valve mechanism is provided in a movable core, and a first valve seat of the first valve mechanism is formed in a second valve portion of the second valve mechanism.
When the movable core is attracted to a fixed core in the aforementioned on/off valve, the first valve portion leaves the first valve seat so as to allow brake fluid to flow from the main hydraulic pressure passage to the stroke simulator.
When the movable core approaches the fixed core, the second valve portion is pulled up by a retention member attached to the movable core. Thus, the second valve portion leaves a second valve seat so as to increase the flow rate of the brake fluid flowing from the main hydraulic pressure passage to the stroke simulator.
The aforementioned brake hydraulic pressure generating device has a configuration as follows. That is, when a brake pedal is operated, the first valve mechanism is opened so that a small amount of brake fluid can flow to reduce the differential pressure between the brake hydraulic pressure on the master cylinder side and the brake hydraulic pressure on the stroke simulator side. On this occasion, the second valve mechanism is opened to increase the flow rate of the brake fluid.
In the aforementioned brake hydraulic pressure generating device, the first valve portion is separated from the first valve seat by the movable core, and the second valve portion is separated from the second valve seat by the same movable core. This configuration must have a space which is large enough for the movable core to make a stroke to open both the first valve mechanism and the second valve mechanism. Therefore, due to increase in the moving amount of the movable core, the on/off valve may increase in size.
In addition, the flow rate in the on/off valve changes in two steps when the brake pedal is stepped down. Therefore, operation feeling of the brake pedal may change.